The invention relates to an injection valve according to the preamble of patent claim 1.
Injection valves conventionally have a valve housing in which, for example, an actuator for controlling a servo valve is provided. The servo valve sets a pressure in a control chamber. Furthermore, the injection valve has a nozzle body which has a sealing seat and injection holes. A recess in which a nozzle needle is guided is made in the nozzle body. The nozzle needle is moved as a function of the pressure in the control chamber.
The recess has a pressure chamber which is connected to a fuel line of the housing. Since a fuel is guided at high pressure in the fuel line, particularly in the case of diesel injection valves, a sealing point is produced between the housing and the nozzle body. The sealing point is preferably sealed by the nozzle body being pressed against the housing. A clamping nut is provided for this purpose, said nut being connected to a thread of the housing and prestressing the nozzle body against the housing. The prestressing of the nozzle body requires large prestressing forces particularly at a high fuel pressure. The prestressing force has to be transmitted by the clamping nut to the nozzle body via an optimized geometry. For this purpose, it is known to form a bearing surface on the nozzle body, which surface is of conical design and tapers in the direction of the tip of the nozzle body.
At the same time, the clamping nut has a conical bearing surface which tapers in the direction of the tip of the nozzle body. A defined differential angle is made between the bearing surface of the nozzle body and the bearing surface of the clamping nut in order to ensure a defined surface pressure. At a very large prestressing force it has been shown that the action of force perpendicular with respect to the longitudinal direction of the nozzle body is relatively large and therefore produces an expansion of the clamping nut in the radial direction. Damage to the clamping nut may occur as a consequence.
The object of the invention is to provide an injection valve in which an optimized transmission of the prestressing force to the nozzle body is achieved.
The object of the invention is achieved by the features of claims 1 and 8. The injection valve according to claim 1 has an optimized transmission of force between the clamping nut and the nozzle body. The optimized transmission of force is achieved by the surface with which the clamping nut rests on the nozzle body being enlarged. The enlarged surface is achieved by a curved shape which is formed either on the clamping nut or on the nozzle body. Owing to the curved shape, instead of a linear contact between the nozzle body and the clamping nut contact in the form of a ring surface is ensured.
The injection valve according to claim 8 has the advantage that the force for prestressing the nozzle body is transmitted via a transmission element. The transmission element permits a lower loading of the clamping nut in the radial direction.
Further advantageous designs of the invention are specified in the dependent claims.
The bearing surface which rests on the curved bearing surface preferably has a conical surface. The conical surface is preferably arranged at an angle of 40xc2x0 and 60xc2x0 with respect to the central axis of the injection valve. The pairing of the curved bearing surface with the planar conical surface provides a cost-effective embodiment.
In a preferred embodiment, the clamping nut has a concave partially spherical surface and the nozzle body has a convex surface. By means of this embodiment, an improved surface contact between the clamping nut and the nozzle body is achieved.
The curved bearing surface preferably has a convex surface. The radius of the convex surface lies preferably in the range from 20 to 60 mm.
In order to support the pressure chamber of the nozzle body, the curved surface is preferably arranged at the height of the pressure chamber, so that the line of action of the prestressing force passes through the pressure chamber. In this manner, at the same time as the nozzle body is pressed against the housing, the pressure chamber is supported from the outside, so that a high compressive strength of the nozzle body is achieved.
An optimum support in terms of pressure of the pressure chamber is achieved by the curved bearing surface being arranged at the height of the center of the pressure chamber.
The clamping nut preferably has a ring part which merges into a sleeve part. The sleeve part is arranged perpendicular with respect to the longitudinal axis of the injection valve. A first bearing surface is arranged on the ring part. In addition, a transmission element is provided which transmits the radial component of the prestressing force of the nozzle body into a virtually axial component which engages on the ring part. The transmission of the radial prestressing force to the ring part of the clamping nut makes it possible to make the sleeve part relatively thin. An overall small diameter of the injection valve is made possible by means of a thin sleeve part.
The transmission element preferably has in cross section the shape of a wedge with a third and fourth bearing surface, the third and fourth bearing surfaces being aligned at an angle of less than 90xc2x0 with respect to each other.
The transmission element is preferably designed in the form of a ring which enables the prestressing force to be transmitted in a manner distributed uniformly around the circumference of the nozzle body.
The transmission element preferably bears against the ring part of the clamping nut, the surface pairing being arranged at an angle of approximately 90xc2x0 with respect to the central axis of the injection valve. At the same time, a second surface pairing, which is arranged between the transmission element and the nozzle body, has an angle of 20 to 40xc2x0 with respect to the central axis of the injection valve.
The abovementioned geometries ensure an improved transmission of the prestressing force.